Carpeting is manufactured from yarns or tows produced from natural or synthetic staple fibers or continuous synthetic filaments, respectively. The fibers are delivered to a yarn spinning plant in bales while the filament is shipped on cones. The yarn maker generally blends all of the bales of staple fiber of a particular lot, through an opening process which consist of mixing portions of each bale in a lot in one or more opening operations and combining the output of these operations, thus, insuring more uniform yarn properties, such as dye acceptance. In some instances the fibers are blended twice, or cross blended as this practice is referred to in the trade. Depending upon the ultimate use of the yarn, various treatments may be undertaken during blending, such as tinting for lot identification and/or application of lubricants and the like. The blended fibers are carded to form a web which is collected as a card sliver. This rope-like card sliver is fed to the first pin drafter therein to produce a sliver, an operation tending to further parallel the individual fibers in the resulting sliver. It is customary for the sliver to be pin-drafted several more times so that the yarn (referred to as singles) subsequently produced will be of the desired weight and, of course, obtain uniformity through further paralleling of the fibers.
The yarn may also consist of an assembly of any number of continuous mono-filaments of varying deniers which are combined and twisted to give continuous multi-filament yarn singles.
Normally these single yarns are plyed, two ply being the most common, by twisting the singles in a reverse direction to the singles twist, a process referred to as cabling. In most modern day carpet mills the yarns are "tufted" through a jute, polypropylene or other woven or non-woven scrim or primary backing on tufting machines which may be and usually are computerized to enable numerous designs both as to length of the loop, type of loop, number of loops per inch, etc. to be made. This assembly can be, and usually is, dyed in one of the numerous batch or continuous dye machines commonly in use today. The so tufted carpet may have the loops pre-cut, if a cut loop pile is desired, and an adhesive, such as latex, urethane or the like, applied and cured onto the back of the carpet to anchor the tufts to the primary backing and then trimmed to the desired width either at this point or before the latex is applied. To provide stability and weight to the carpet, a secondary backing of jute, polypropylene, or the like, may be attached at this time.
Recently several of the mills have begun to blend or have blended a small amount of a conductive fiber into the yarn to act as a static dissipation element. It is becoming conventional for the fiber manufacturer to add a wad of individual fibers to the bales. Such fibers are composites made conductive by incorporating into a hollow fiber a core of carbon (graphite) or by coating a fiber with a sheath made of a composite containing carbon (graphite) among other methods. These electroconductive fibers are blended with the polymer fibers at the staple cutting stage. However in some instances these composite fibers after being made into staples are added to the synthetic staple fibers at the opening stage. In most instances while electrostatic charges are dissipated to some degree when either of the aforedescribed electroconductive fiber (sheath coated or hollow fiber filled with carbon (graphite)) composites is employed, only modest results are achieved.
It would therefore be advantageous for the carpet manufacturer to have a better conductor and a more readily incorporable technique for placing the conductive fiber (carbon or graphite) into the yarn to obtain a more uniform distribution and greater assurance that the contact with a substantial number of tufts, loop or pile of the carpet assembly are made to carry the static charge away from the source, i.e., distribute the charge over a large area of the carpet.